How farmers can reduce herbicide drift

Farmers can cut down on herbicide drift by using low-volatility herbicide blends, which are less likely to turn to vapors, and use a nozzle design on the sprayer that produces larger droplets that do not easily drift in the wind, as well as spray on less windy day. (Credit: Chafer Machinery/Flickr)

Farmers should work to reduce herbicide drift when spraying fields, researchers urge, as the chemicals create a variety of unintended consequences on neighboring fields and farms.

The researchers found a range of effects—positive, neutral, and negative—when they sprayed the herbicide dicamba on fields that are no longer used for cultivation and on field edges, according to J. Franklin Egan, research ecologist, USDA-Agricultural Research Service. He says the effects should be similar for a related compound, 2,4-D.

Because dicamba and 2,4-D typically target broadleaf plants, such as wildflowers, and not grasses, the researchers found that the number of wildflowers diminished, while grasses soon dominated the field edges, which were once blends of broad leaf plants and grasses. (Credit: Penn State)

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“The general consensus is that the effects of the increased use of these herbicides are going to be variable,” says Egan. “But, given that there is really so much uncertainty, we think that taking precautions to prevent herbicide drift is the right way to go.”

Farmers are expected to use dicamba and 2,4-D on their fields more often because biotechnology companies are introducing crops genetically modified to resist those chemicals. From past experience, 2,4-D and dicamba are the herbicides most frequently involved in herbicide-drift accidents, according to the researchers.

Because the herbicides typically target broadleaf plants, such as wildflowers, they are not as harmful to grasses, Egan says. In the study, the researchers found grasses eventually dominated the field edge test site that was once a mix of broadleaf plants and grass. The old field site showed little response to the herbicide treatments.

Herbicides and pests

Herbicide drift was also associated with the declines of three species of herbivores, including pea aphids, spotted alfalfa aphids, and potato leaf hoppers, and an increase in a pest called clover root curculio, Egan says. The researchers found more crickets, which are considered beneficial because they eat weed seeds, in the field edge site.

The researchers, who report their findings in the current issue of Agriculture, Ecosystems and Environment, did not see a drop in the number of pollinators, such as bees, in the fields. However, the relatively small size of the research fields limited the researchers’ ability to measure the effect on pollinators, according to Egan.

“That may be because pollinators are very mobile and the spatial scale of our experiment may not be big enough to show any effects,” Egan says.

Reducing drift

Farmers can cut down on herbicide drift by taking a few precautions, according to Egan. They can spray low-volatility herbicide blends, which are less likely to turn to vapors, and use a nozzle design on the sprayer that produces larger droplets that do not easily drift in the wind.

Egan also recommended that farmers follow application restrictions printed on herbicide labels and try to spray on less windy days when possible.

The tests were conducted on two farms in Pennsylvania. One field edge site was located near a forest and alfalfa field. The old field was an acre plot near Penn State’s Russell E. Larson Agricultural Research farm.

Additional scientists at Penn State and Sarah Goslee, a US Department of Agriculture ecologist, contributed to the work, which received support from the Environmental Protection Agency.